Light projection systems are used in spotlights, picture projection systems, and other applications. Some major objectives in the design of such systems are the need to minimize heating and to dissipate what heat is generated. Another major objective in many cases is to reduce the physical size of the system. In some applications there is a need to achieve uniform distribution of light over the area being illuminated and, in most applications, there is a need to provide for safe replacement of lamps.
The systems that are made possible by this invention are concerned with lamp replacement safety to the extent that they are compatible with and can incorporate the safe lamp handling system and apparatus. The systems of the invention are directly concerned with, and they achieve, efficiency, heat control, packaging size, and illumination uniformity.
Illumination uniformity is particularly important in motion picture projection, especially in creating special effects during picture production. It is difficult to illuminate the marginal portions of a picture to the level of central region illumination. When the final scene includes projection of a photographed background, the degree of non-uniformity is multiplied. Some scenes in the motion picture Star Wars were photographs of photographs of photographs --more than two dozen times. Non-uniformity is multiplied two dozen times. That severely limits the film maker's ability to make special effects look real, and it forces him to concentrate story telling and mood setting at picture center.
Even after the film has been produced, the effectiveness with which it can be displayed on large, wide screens depends heavily on the effectiveness of the light system to illuminate the margins of the projector's film gate.
Practical light sources are omnidirectional and generate infra-red as well as visible rays. Those factors combine, when high light intensity output is required in one direction, to make it necessary to use reflectors. When it is desired that output light rays be directed along parallel output paths, a parabolic reflector is used. On the other hand, if the output light rays are to converge to a focal point, an elliptical relfector is used. For reflection of a given fraction of the available light, the parabolic reflector has the largest diameter. The elliptical reflector has smaller diameter and the diameter is decreased as the distance to the focal point is decreased. In the prior art, reduction in reflector diameter is achieved by shortening the distance to the focal point, which complicates lens design if an image of the light source is to be projected uniformly, or by reducing diameter and losing the light that would be reflected from the outer margins of the reflector In practice, both of these expedients are employed in a compromise between output intensity, lens system complication, and uniformity of intensity across the output beam.
Except in arrangements that produce a central shadow, the light output from a reflector is always more intense at the central region of the output beam. Unless intensity is modified in some fashion, images of the source seen after reflection are less intense away from the center. The effect of that can be made less apparent to a viewer by increasing source light intensity, but to do that multiplies the heat dissipation problem. Increasing source intensity cannot overcome the effect of non-uniform intensity when projecting the composite of multiple projections.